Cerebral microvascular endothelial cell Na-K-Cl cotransport: Regulation by astrocyte-conditioned medium

Martha E O'Donnell, A. Martinez, D. Sun

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65 Scopus citations


Brain microvascular endothelial cells play an important role in regulation of ion and fluid movement between the blood and the brain interstitium. Astrocytes have been shown to induce blood-brain barrier properties in the endothelial cells, including formation of tight junctions and increased expression and asymmetric distribution of enzymes and ion transport systems. Previous studies have demonstrated that endothelial cells of bovine aorta possess a highly active Na-K-Cl cotransport system that participates in intracellular volume regulation. The present study was conducted to evaluate Na-K-Cl cotransport activity of cerebral microvascular endothelial cells and to determine whether astrocyte-conditioned medium (CM) influences Na-K-Cl cotransport activity of these cells. We found the brain microvascular endothelial cells to exhibit a robust Na-K-Cl cotransport activity, comprising 50% of the total K influx. Activity of the cotransporter was stimulated by agents that elevate intracellular Ca and by hypertonicity and was inhibited by agents that elevate adenosine 3',5'-cyclic monophosphate, guanosine 3',5'-cyclic monophosphate, or activate protein kinase C. Exposure of the cells to primary astrocyte- or C6 glial cell-CM but not A7r5 or A10 vascular smooth muscle cell-CM also increased cotransport activity. However, this effect required > 1 h of exposure to CM, was additive with the effects of vasopressin, calcium ionophore, and hypertonicity, and was blocked by the protein synthesis inhibitor cycloheximide. These findings are consistent with the hypothesis that expression of endothelial cell Na-K-Cl cotransport is induced and/or maintained by astrocytes and that the cotransporter may be an important component of blood-brain barrier function.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Cell Physiology
Issue number3 37-3
StatePublished - 1995


  • aortic endothelial cells
  • bumetanide
  • C6 glial cells
  • cultured cerebral microvascular endothelial cells
  • hypertonicity
  • osmolarity
  • primary astrocytes
  • regulation of intracellular volume
  • regulatory volume increase

ASJC Scopus subject areas

  • Cell Biology
  • Clinical Biochemistry
  • Physiology
  • Agricultural and Biological Sciences(all)


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